The present invention relates to a three-section pump of a type including a variable displacement piston pump and an additional rotary pump providing a separate supply of output fluid under pressure. More particularly, the invention relates to such a pump assembly wherein a centrifugal pump is employed for supercharging the variable displacement piston pump.
Variable displacement piston pumps have been commonly employed to deliver fluid under pressure to operate implement systems. The variable displacement piston pump is particularly suited for such applications because of the accurate control permitted over output flow. In addition, the variable displacement piston pump tends to require minimum horsepower when the implement system is in a neutral condition and is not receiving output fluid from the pump.
It is also well known to employ an additional pump, preferably a centrifugal pump, for delivering input fluid to the variable displacement piston pump in order to assure "positive filling" of the variable displacement pump cylinders. Accurate control is thus achieved over output pressure of the variable displacement pump.
Many hydraulic circuits or implement systems require more than one source of fluid under pressure and it is common to provide multiple pumps for such applications. The use of multiple pumps often presents a design problem because of limited available space. This design problem is often even more marked because of the need to provide rugged, simple construction for the pumps and conduits interconnecting the pumps with the hydraulic circuit for the implement system.